Electrophotography generally includes the steps of forming an electrostatic latent image on a photoconductive photoreceptor by any of various methods, subsequently making the latent image visible using a toner for electrostatic-image development (hereinafter abbreviated to “toner”), thereafter transferring the visible toner image to a receiving material, e.g., paper, and fixing the toner image by heating, pressing, etc. Various methods are known as these steps, and methods suitable for the respective image forming processes are being adopted.
Known toners include: a two-component toner configured of a carrier and a toner; and a one-component toner in which no carrier is required (magnetic toner, nonmagnetic toner). The nonmagnetic toner contains a binder resin as a main component, while the magnetic toner contains a binder resin and a magnetic powder as main components. A colorant (pigment), charge control agent, wax, etc. are further contained dispersedly therein besides the binder resin.
As shown in FIG. 1, a toner cartridge which contains a toner therein is equipped with a developing roller 3 for supporting the toner 1 thereon, a charging member (charging blade) 2 disposed on the upper side of the developing roller 3, a retaining blade 4 disposed on the lower side of the developing roller 3 so as to face the developing roller 3 at a predetermined distance, a photoreceptor 7 to which the toner 1 supplied by the developing roller 3 is transferred, a charging roller 5 which has been disposed on the upper side of the photoreceptor 7 and which charges the photoreceptor 7, and a cleaning member (wiper blade) 6 which has been disposed below the charging roller 5 and which removes any toner remaining on the photoreceptor 7. The charging member (charging blade) 2 serves not only to control the amount of the toner 1 to be supported on the surface of the developing roller 3 and conveyed to the photoreceptor 7 but also to frictionally charge the toner 1.
As shown in FIG. 2, the toner cartridge of FIG. 1, i.e., the toner cartridge having a configuration wherein the charging member (charging blade) 2 has been disposed on the upper side of the developing roller 3, is disposed on the upper side of the intermediate transfer belt 9 in an image forming apparatus. In FIG. 2, numeral 10 denotes a transfer roller, which serves to transfer an image to the transfer roller 10, the image having been transferred to the surface of the intermediate transfer belt 9 by successively superposing toners supplied by four toner cartridges 8 which have been disposed on the upper side of the intermediate transfer belt 9 and in which toners of four colors (yellow, magenta, cyan, and black) are contained.
Besides such cartridges, there is a toner cartridge in which a charging member and a retaining blade have been disposed in an arrangement which is vertically reverse to that in the toner cartridge shown in FIG. 1. Namely, as shown in FIG. 3, this toner cartridge includes a charging member (charging blade) 16 disposed on the lower side of the developing roller 12 and a retaining blade 11 disposed on the upper side of the developing roller 12. Incidentally, in the toner cartridge shown in FIG. 3, the toner 13 retained below the developing roller 12 is supplied to the developing roller 12 by means of a stirring blade 15 and a feed roller 14 disposed so as to be in sliding contact with the developing roller 12. Like the toner cartridge shown in FIG. 1, the toner cartridge shown in FIG. 3 is equipped with a photoreceptor 17 to which the toner supplied by the developing roller is transferred. The toner cartridge shown in FIG. 3 is equipped with the photoreceptor 17, a charging roller 19, and a cleaning member (wiper blade) 18 which has been disposed above the charging roller 19 and which removes any toner remaining on the photoreceptor 17, so that the arrangement of these members is reverse to that in the toner cartridge shown in FIG. 1.
As shown in FIG. 4, the toner cartridge of FIG. 3, i.e., the toner cartridge having a configuration wherein the charging member (charging blade) 16 has been disposed on the lower side of the developing roller 12, is disposed on the lower side of the intermediate transfer belt 21 in an image forming apparatus. In FIG. 4, numeral 22 denotes a transfer roller, and 20 denotes four toner cartridges 20 which have been disposed on the lower side of the intermediate transfer belt 21 and in which toners of four colors (yellow, magenta, cyan, and black) are contained.
In general, image failure items directly attributable to toners include ghost, dust (fogging), following-up failure, density unevenness, decrease in density, and the like. Disclosed in patent document 1, as a measure against these image failures, is a toner which has specific shape properties imparted thereto and has a transportability index regulated so as to be within a specific range and which therefore stably gives images of high quality.